1. Field of the Invention
This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of structures and methods for grounding a microactuator to a suspension in a dual stage actuated (DSA) suspension.
2. Description of Related Art
As the track densities of hard disk drives (HDDs) continue to increase, the need to position the data read/write head over the spinning disk platter quickly and accurately has likewise increased. Dual stage actuated (DSA) suspensions have been developed in order to accommodate the demand for more expedient and accurate positioning of the read/write head.
In a DSA suspension, as for example in U.S. Pat. No. 7,459,835 issued to Mei et al. as well as many others, in addition to a voice coil motor which moves the entire suspension, at least one additional microactuator is located on the suspension in order to effect fine positional movements of the magnetic head slider keeping it properly aligned over the correct data track on the spinning disk. The microactuator(s) provide much finer control and higher bandwidth of the servo control loop than would a voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible. In the discussion that follows, for simplicity the microactuator will be referred to simply as a “PZT,” although it will be understood that the microactuator need not be of the PZT type.
DSA suspensions in which the PZT is located at or near the suspension gimbal are called gimbal-based DSA suspensions, or simply GSA suspensions. Generally speaking, GSA suspensions provide higher servo bandwidth than do DSA suspensions in which the PZT is located at the base plate or on the body of the load beam.
Without admitting that FIG. 1 is “prior art” within the legal meaning of that term, FIG. 1 is a bottom plan view of a prior GSA suspension 10 designed by the assignee of the present application, and FIG. 2 is a cross sectional view of the suspension of FIG. 1 taken along section line A-A′, showing the details of the PZT mechanical and electrical bonding to the flexure. As used herein the term “bottom” refers to the side of a suspension or part thereof that faces the data storage disk, and “top” refers to the side of a suspension or part thereof that faces away from the data storage disk. The bottom side of a suspension is sometimes referred to as the slider side. The bottom side of the suspension and its components are therefore oriented toward the top of FIG. 2, and the top side of the suspension and its components are oriented toward the bottom of the figure.
Additionally, as used herein the term “proximal” means toward to the actuator arm to which the suspension is mounted, and “distal” means toward the cantilevered end of the suspension to which the head slider is mounted.
In the figure, suspension 10 includes a load beam 12 and a flexure 20 affixed at the distal end 11 of load beam 12, typically by laser spot welding. Flexure 20 typically includes a metal support layer 24 which is typically stainless steel, an insulating layer 28 which is typically polyimide, and a signal conducting layer 30 of copper or copper alloy that includes various individual traces carrying information signals and voltages. Gold plating 32 over an exposed portion of the copper signal conducting layer 30 defines a gold contact pad 32 which carries the driving voltage for a PZT 70. A read/write head slider 60 is attached at a distal end 11 of suspension 10, on a gimbal tongue 62 which is part of a gimbal 40 on flexure 20. Gimbal 40 is formed from the stainless steel support layer 24, and includes PZT connector arms 42. Gimbal 40 allows head slider 60 to pitch, yaw, and roll freely as it travels over the disk platter to accommodate disk surface irregularities and vibrations.
PZT motor 70 includes a PZT element 74 together with top and bottom metallized surfaces on their respective top and bottom faces which form ground electrode 78 and driven electrode 76, respectively.
Driven electrode 76 on the bottom of PZT 70 is connected to gold plated contact pad 32 which provides the PZT driving signal or voltage, through conductive adhesive 48 which forms an electrically conductive bridge. Conductive adhesive 48 is typically a flowable hardenable conductive adhesive such as silver-containing conductive epoxy. Non-conductive adhesive 46, typically a non-conductive epoxy, provides the primary structural bonding and provides electrical insulation.
PZT top electrode 78 is electrically connected to the flexure's stainless steel layer 24 which is connected to ground, through conductive epoxy 50. Conductive epoxy 50 is sandwiched between PZT 70 and the gold plated pad 25 on stainless steel layer 24 of flexure 20.
Bottom electrode 76 of PZT 70 is thus the driven electrode which is connected to the driving voltage through a conductive epoxy bridge 48, and the top electrode 78 is the ground electrode that is connected to the grounded stainless steel body of flexure 20 through conductive epoxy 50 sandwiched between PZT 70 and stainless steel 24. Conductive epoxies 48 and 50 are typically cured by convection, and more typically by a heated air stream, although other types of adhesive such as UV-cured epoxy can be used.
When an actuation voltage is applied at gold contact pad 32, PZT 70 expands or contracts depending on whether the applied voltage is positive or negative. The proximal end of PZT 70 which is on the left side in the figure is relatively fixed, and the distal end which is on the right side of the figure is relatively freely moving. Actuation of PZT 70 thus causes the distal end of the PZT to move, which effects fine positional movements of head slider 60.